A germanium single-crystal wafer comprises silicon with an atomic concentration of from 3×1014 atoms/cc to 10×1018 atoms/cc, boron with an atomic concentration of from 1×1016 atoms/cc to 10×1018 atoms/cc, and gallium with an atomic concentration of from 1×1016 atoms/cc to 10×1019 atoms/cc. Further provided are a method for preparing the germanium single-crystal wafer, a method for preparing a germanium single-crystal ingot, and the use of the germanium single-crystal wafer for increasing the open-circuit voltage of a solar cell. The germanium single-crystal wafer has an improved electrical property in that it has a smaller difference in resistivity and carrier concentration.